Check engine light
Check engine light on? Start here.
If the light is flashing, stop driving first. If it is steady, read the codes before you clear anything or buy parts.
Flashing light? Stop driving.
A flashing check engine light means stop driving, to avoid damaging the catalytic converter. Have the car checked by a professional.
Also stop and see a professional (and don't keep driving) for anything involving:
- the brakes or steering
- airbag or other occupant-safety warnings
- a fuel leak or a smell of fuel
- a hybrid or electric vehicle's high-voltage system (orange cables)
- engine overheating or a low oil pressure warning
A steady light: read the codes first
- Find the port. The OBD-II port is usually under the dashboard, near the steering column.
- Plug in an adapter and turn the ignition on. Start the engine, or turn the key to ON or RUN.
- Read the codes and the freeze frame. Write them down before you change anything.
Using a laptop? See how to connect an ELM327 adapter on Windows, macOS or Linux.
What the scan shows
- Stored codes: confirmed faults that turned the check engine light on.
- Pending codes: faults that are not confirmed yet. They become stored if the fault repeats.
- Permanent codes: recorded by the car's computer. A scan tool cannot clear them.
- Freeze frame: the sensor snapshot from the moment the fault was recorded.
To decode the letters and numbers, see how to read a trouble code.
Don't clear the codes first
Clearing erases stored and pending codes and turns the light off. Permanent codes stay until the car passes the relevant drive cycle on its own.
Clearing also resets the emissions readiness checks, and disconnecting the battery leaves them incomplete too. The car may fail an emissions test until it has been driven enough for them to complete again.
If a stored code comes straight back after clearing, that points to an active fault.
Confirm the cause before you buy parts
A failure in one component can set a code in another, so don't settle on one cause from a single reading. Rank the possible causes by likelihood, then run the simplest, cheapest test that would confirm the cause before you buy a part.
How DeepDiag helps
- Reads your trouble codes: from the engine and emissions controllers, and from ABS, airbag and body modules where the vehicle allows it.
- Explains them in plain language: what the data shows, what the AI suspects, and how confident it is.
- Says whether you can fix it yourself: a rough time and cost estimate, and when to stop and see a professional.
- Helps you confirm before you buy parts: suggested checks to pin down the cause first.
- Checks emissions readiness: so you know whether the car is ready for a smog test.
DeepDiag gives an AI-assisted reading of the data your car reports. It isn't a professional inspection, a safety check or a guarantee, and the AI can be wrong. Every feature needs an active Premium subscription.
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